1. Field of the Invention
This invention relates broadly to apparatus for protecting occupants of vehicles in crashes or sudden drops. More specifically, it relates to apparatus that can be adjusted for optimum performance relative to the weight of the individual occupant and his associated equipment, and to a method for making such apparatus.
2. Description of the Prior Art
Because of the relatively low tolerance of the human body to forces parallel to the spine, survivable helicopter accidents, in which sufficient living space is provided by the structure, may impose injurious forces in the vertical direction. Because insufficient crush space is available within the floor structure of helicopters and light aircraft, the seat must play a significant role in attenuating these potentially injurious forces to tolerable levels. Recently developed helicopters such as the U.S. Navy's SH-60B Seahawk, and U.S. Army's UH-60A Black Hawk, and the AH-64A Advanced Attack Helicopter are equipped with seats that have builtin vertical energy-absorption systems.
Presently, fixed energy absorber limit loads are set for the 50th-percentile occupant, under the crash conditions of the 95th-percentile survivable accident. A heavy (e.g. 95th-percentile) occupant in the same crash conditions may bottom out at the end of the stroking distance. Conversely, a lightweight (e.g., 5th-percentile) occupant will not be able to take advantage of the full stroking distance available and will be subjected to accelerations of higher magnitude than desirable.
Prior practice generally has been to build energy absorbers with fixed load capability, with the magnitude of the load set for one particular occupant weight. Occupants of other weights were therefore subjected to energy absorber loads which are not optimized. The only variable-load energy absorber known to the applicants is a device built for CH-47 helicopters. This device utilizes a wire-bending machinism whereby variations in load are achieved by engaging different wires with bending mechanisms. Disadvantages of this device are that the load can be varied in only a few specific increments, and that the system is relatively heavy and bulky.